The present invention relates to X-Y plotters and, more particularly, to guide rollers for guiding a carriage carrying the pen block of the plotter along the track thereof, wherein the wheels on one edge are releasably mounted to allow the carriage and pen block to be removed from the track easily when desired.
The basic environment of the present invention is illustrated in FIG. 1 in simplified form. A plotter, generally indicated as 10, includes a track 12 disposed parallel to and traversing the path of a sheet of paper 14 (or other media) adapted to be moved longitudinally back and forth beneath the track 12 in the direction of arrows 16 by any of several means (not shown). A pen block carriage 18 for carrying a pen block 19 attached thereto is mounted on the track 12 for longitudinal movement in either direction as indicated by the arrows 20. The carriage 18 is connected to a metal tape 22 passing around the two pulleys 24 disposed on respective ends of the track 12. As the pulleys 24 or tape 22 are driven in either direction (by means not shown) as indicated by the arrows 26, the pen block 19 and carriage 18 are moved in the direction of arrows 20. The pen block 19 carries a pen 28 (or other writing instrument) in contact with the paper 14. As the paper 14 is moved in the direction of arrows 16 and the pen block 19 is moved in the direction of arrows 20, the pen 28 is caused to mark the plot 30 on the paper 14.
In order to provide precision and repeatability in the performance of the plotter 10, the tolerances associated with the parts comprising the carriage 18 and track 12, in particular, are quite exacting. It is typical to provide wheel sets (not shown) at the four corners of the carriage 18 (as FIG. 1 is viewed) bearing against the rear edge 32 and front edge 34 of the track 12 to guide the carriage 18 repeatably in a predetermined path along the track 12. Further, it is known to configure the front and rear edges 32, 34 at an angle (typical between 60.degree. and 120.degree.) and to mount the wheel seats in an angularly matched orientation so as to hold the carriage 18 onto the track 12 against movement in any direction except longitudinally along the track 12 in the direction of arrows 20. In the prior art apparatus employing such a carriage guide arrangement, a small amount of contaminants on one or both of the edges 32, 34 can cause the carriage 18 to bind in its movement on the track 12 to the detriment of the accuracy of the plot being made since the guides are not automatically adjustable. Moreover, in order to remove the carriage 18 and pen block 19 from the track 12 for maintenance (such as removing the contaminants) the process is complex, bothersome, and prone to the introduction of errors in reassembly.
Wherefore, it is the object of the present invention to provide a releasable pen block carriage guide which is easily releasable to allow the pen block to be removed easily from the track for maintenance.
It is yet another object of the present invention to provide a releasable pen block carriage guide which is automatically adjustably.